Polymers prepared from the aromatic compounds, such as terephthalic acid, p-aminobenzoic acid, and p-phenylenediamine exhibit excellent physical properties, but the polymers are not biodegradable. Polyesters derived from terephthalic acid, such as polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT), and poly(1,4-butylene terephthalate) (PBT) are used extensively for making fibers and molding articles. Some of these are polymers that are used in biomedical applications such as non-absorbable surgical sutures, and these polymers are considered to be safe and biocompatible. Unfortunately, these polymers are non-absorbable and, therefore, cannot be used as absorbable sutures or as absorbable polymers for the controlled release of drugs.
Due to the availability and numerous uses of the polymers derived from these aromatic compounds, it is desirable to enhance their value, for example, by functionalizing these aromatic compounds and preparing absorbable polymers therefrom. The resulting absorbable polymers should have a specific controlled degradation profile or range enabling controlled release of drugs over an extended, controllable time range when physically admixed with these polymers.
Synthetic absorbable polymers have been used to produce various surgical products such as sutures, implants, prostheses, and the like, for several years. Illustrative U.S. patents describing such polymers include U.S. Pat. Nos. 3,297,033; 3,044,942; 3,371,069; 3,531,561; 3,636,956; Re. 30,170; and, U.S. Pat. No. 4,052,988.
Implantable surgical devices must be sterile prior to implanting in the body. Sterilization of devices is usually accomplished by the use of heat, ethylene oxide, or gamma radiation using a 60Co source. In many cases, the use of gamma radiation is the most convenient and most certain way to effect sterilization. However, all of the synthetic absorbable polymers now in commercial use are significantly degraded by gamma radiation. Therefore, unless for some reason degradation of the polymer is desired (for instance, to greatly accelerate the absorption rate), the use of gamma radiation is precluded for the purpose of sterilizing the presently commercial synthetic absorbable polymers.
This invention also provides a new class of polymers that are absorbable and which are expected to be sterilizable by gamma radiation while still retaining a desirable level of physical and biological properties.